In many fields, such as in the medical sciences, an experienced person is required to analyze brain waveforms for certain characteristics and provide corresponding conclusions. An experienced analyzer often uses a set of decision making criteria when deciding whether or not a brain waveform exhibits a particular characteristic. The skilled person many times analyzes waveform slope, latency, amplitude, intertrial reproducibility, and other specific morphologic patterns. Various apparatus and computer programs are available to aid the waveform analyzer with such analysis.
One example of waveform analysis of electrical brain signals is when a clinician tests the hearing of a patient. In order to test the hearing of young children or infants, or of adults who cannot respond to an audiologist testing the hearing response, a clinician can measure the auditory brain stem response (ABR) of the patient. By analyzing a visual display of the waveform of the auditory brain stem response, a clinician can often determine from the characteristics of the waveform whether the patient has a hearing problem. Other physiological and brain related dysfunctions can also be detected, diagnosed or monitored by visually analyzing the waveform display.
An auditory brain stem response of a patient is obtained by placing electrodes at the vertex or crown of the head and behind the left and right ear of the patient. A click generator is employed to produce a clicking sound which is coupled to the patient's ears. The electrical signals generated by the brain and received by the electrodes are utilized to provide a visual display of the brain activity in response to the auditory stimulus. The clinician can then analyze the ABR waveform in order to determined whether there was any conscious or subconscious response to the audio clicking stimulus. In analyzing an ABR waveform and deciding whether the waveform contains a pattern which indicates a response to the audio stimulus, the experienced clinician carefully examines all the characteristics of the waveform to determine the presence or absence of waves well defined in this area, such as Waves I, II, III, IV and V. The presence or absence of each such wave signifies the ability of a person's brain to assimilate input audio stimulus and react accordingly.
Various apparatus and computer programs have been developed in an attempt to simplify brain waveform analysis. Such equipment is intended to provide results which replace the subjective decisions of the clinician, and thereby save the clinician from the time consuming and often strenuous task of brain wave analysis. Typically, such apparatus and computer programs are adapted to detect brain wave peaks which exceed a certain thresholds to determine whether the waveform indicates a certain response. Other computerized equipment is available for comparing measured brain waveforms with normal brain waveforms to determine whether an abnormality exists.
U.S. Pat. No. 4,275,744, by Thorton et al., and U.S. Pat. No. 4,545,388, by John, provide two examples of prior art for analyzing brain waves. In the Thorton et al. patent, audio frequency pulses are applied to the ear of the person being tested. Each audio stimulus is realized as a characteristic response in the form of an electroencephalographic (EEG) waveform produced by the subject. The EEG signal is then transmitted through a signal conditioner and then applied to a signal sampling device which samples the signal for responses at predetermined times. The predetermined times are selected by looking at the times that such a response occurs in an exemplary waveform. However, the operator then must determine the ratio of the number of pulses to the number of trial pulses over a selected period of time to provide a measure of the likelihood that a response is being evoked in a subject by the auditory signals. According to the teachings of the noted patent, the apparatus does not analyze the waveform and make decisions, rather the apparatus supplies the operator with specific data and the operator must then determine whether a response is being evoked in a patient by the auditory signals.
The John patent describes a technique for monitoring the state of a patient's brain during a medical procedure relative to a self-norm established at an earlier time. The self-norm is formed by electrical measurements taken of brain functions which are selected for medical relevance to the particular medical procedure. During the medical procedure, the same brain functions are electrically measured. Each new set of measurements is tested for statistically and medically significant changes from the self-norm and, if a test shows such a change, an indication is produced. The indication shows not only that a change has occurred, but also the ascribed medical significance of the change itself and the persistence of a change. Obviously, one major drawback to the technique is that if emergency medical procedures are necessary, it is unlikely that self-norm measurements are also available. Furthermore, although the method and apparatus can detect changes from the self-norm, the method and apparatus does not indicate whether the self-norm is in fact normal.
From the foregoing, it can be seen that a need exists for an on-line procedure which mathematically analyzes waveform morphology characteristics and which emulates the analysis of the experienced waveform analyzer in making particular determinations regarding certain waveform responses. Another need exists for an automatic waveform analysis technique which receives brain waveform data, carries out an analysis according to a hierarchy or predetermined criteria, and provides a positive visual identification of the desired wave if such criteria is satisfied.